Coccidiosis. The Disease is caused by Eimeria species. Pathogenicity is influenced by host genetics, nutritional factors, concurrent diseases, age of the host, and species of the coccidium. Eimeria necatrix and Eimeria tenella are the most pathogenic in chickens.

Mites in chickens. The most economically important of the many external parasites of poultry are mites of the families Dermanyssidae (chicken mite, northern fowl mite, and tropical fowl mite) and Trombiculidae (turkey chigger).

Fungal Diseases

Aspergillosis. The disease is caused by Aspergillus fumigatus. However, several other Aspergillus spp may be incriminated. High mortality rates are seen in chicks and poults that inhale large numbers of spores during hatching in contaminated incubators or when placed on the mold-bearing litter. In older birds, infection is caused primarily by inhalation of spore-laden dust from contaminated litter or feed or dusty range areas.